Control system for vehicles

ABSTRACT

A system for controlling flight of an aircraft has sensors, a receiver, and a digital control system, all of which are carried aboard the aircraft. The sensors determine the position of the aircraft relative to the earth and the inertial movement of the aircraft. The receiver receives transmitted data communicating the position and movement of a reference vehicle relative to the earth. The control system calculates the position and velocity of the aircraft relative to the reference vehicle using the data from the sensors and the receiver and then commands flight control devices on the aircraft for maneuvering the aircraft in a manner that maintains a selected position and/or velocity relative to the reference vehicle. The system allows use of a graphical or tactile user interfaces.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.10/575,223, filed 21 Nov. 2007, titled “Control System for Vehicles,”which claims the benefit of International Application No.PCT/US04/09080, filed 25 Mar. 2004, titled “Control System forVehicles,” both of which are hereby incorporated by reference for allpurposes as if fully set forth herein.

GOVERNMENT LICENSE RIGHTS

The U.S. Government has a paid-up license in this invention and theright in limited circumstances to require the patent owner to licenseothers on reasonable terms as provided for by the terms of Contract No.N00019-98-C-0051.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates in general to the field of control systemsfor vehicles. In particular, the present invention relates to a controlsystem for causing a vehicle to have a selected position or selectedvelocity relative to a reference vehicle.

2. Description of Related Art

Remote control of an aircraft is typically done by commanding theairspeed or inertial speed (groundspeed) of the vehicle, and thedirection of the velocity is selected by controlling the heading of thevehicle. The control inputs are usually commands given in terms of thelongitudinal, lateral, or directional axis of the aircraft. Therefore,if an operator controlling the aircraft wants the aircraft to move in acertain direction, the operator must know in which direction theaircraft is pointing to determine which axis of control must be used,and in which direction, in order to make the aircraft move in thedesired direction. When controlling the aircraft relative to anothermoving vehicle, the operator must also know the velocity and directionof the moving vehicle.

Several methods of controlling vehicles relative to another vehicle havebeen used, including using sensors on the controlled vehicle todetermine the proximity or position of the reference vehicle. Thismethod has been used in, for example, automotive cruise-control systems,such as those disclosed in U.S. Pub. Nos. US 2002/0072843 and US2003/0004633. In U.S. Pat. No. 5,768,131, a radar system carried on thecontrolled vehicle is used to measure the distance and speed relative tovehicles in front of the controlled vehicle. Other systems have includedcameras, such as U.S. Pat. No. 6,324,295 to Valery, et al., or a lightsource and reflector, such as U.S. Pat. No. 5,530,650 to Biferno, etal., used for determining relative positions and motions of aircraftduring refueling.

Although there have been significant developments over the years in thearea of remote control of aircraft and other vehicles, considerableshortcomings remain. If an operator wants to operate a controlledvehicle relative to a moving object, such as another vehicle, theoperator must consider the position and velocity of both the controlledvehicle and the object, making controlling the controlled vehicle a moredifficult task.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, includingits features and advantages, reference is now made to the detaileddescription of the invention taken in conjunction with the accompanyingdrawings in which like numerals identify like parts, and in which:

FIG. 1 is a perspective view of a ship and an aircraft that is beingcommanded by a flight-control system according to the present invention;

FIG. 2 is a perspective view of a landing pad located on the ship ofFIG. 1;

FIG. 3 is a perspective view of a ground control station of the presentinvention;

FIG. 4 is a perspective view of a flight control box of the presentinvention;

FIG. 5 is schematic view of the components of a flight control system ofthe present invention;

FIG. 6 is a view of a first graphical display on the ground controlstation of FIG. 3;

FIG. 7 is a view of a second graphical display on the ground controlstation of FIG. 3; and

FIG. 8 is a schematic flowchart showing the steps of a method of theinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention provides a system for controlling a controlledvehicle in relation to a reference vehicle using relative velocities,which are determined by comparing the position and movement of thecontrolled vehicle with the position and movement of a known point.

For purposes of illustrating the system of the invention, the systemwill be described in reference to its use as a control system for anaircraft operating in conjunction with a ship at sea. The known point onthe ship may be a touchdown point (TDP) for landing the aircraft. Therelative velocity is zero if the aircraft is moving at the samevelocity, i.e., same speed and direction, as the TDP. This inventionallows precise aircraft velocity control relative to the TDP regardlessof the speed of the TDP or the velocity and direction of the relativewind. A unique characteristic of this system is that the control of theaircraft velocity is independent of the aircraft heading, as the systemallows an operator to be able to control the aircraft relative to amoving vehicle in a manner similar to the way that groundspeed iscontrolled relative to a point on the ground. As used herein, “velocity”will be understood as a vector, incorporating both a direction and amagnitude, though these may be discussed independently.

Though the system of the invention is described in use with anaircraft/ship combination, the system may be used for any combinationand number of land, air, or sea vehicles or other moving objects whereit is useful to control the position and velocity of a vehicle relativeto a movable point or vehicle. Some examples of applications include useby a ground vehicle to control aircraft, by aircraft to control groundvehicles, by aircraft to control other aircraft, and by ground vehiclesto control other ground vehicles.

Referring now to FIGS. 1 and 2, an aircraft 11 is depicted as flyingnear a ship 13. While shown in FIG. 1 as an unmanned tiltrotor-typeaircraft, aircraft 11 may be of any type, and may be a fixed wingaircraft or other varieties of rotorcraft, and may be manned andcontrolled by a pilot. FIG. 2 shows a landing pad 15, which is locatedon deck 17 of ship 13 and used for launching and/or recovering aircraft11. Though landing pad 15 is considered the TDP, the movement of landingpad is not independent of the movement of ship 13. Therefore, ship 13 isconsidered a “reference vehicle” for determining the position andvelocity of aircraft 11 relative to ship 13, and the movement of the TDPand ship 13 may be used interchangeably.

In order to control aircraft 11 during flight or launch/recovery, aremote piloting system is used in conjunction with a semi-autonomouscontroller carried on aircraft 11. Referring to FIGS. 3 and 4, theoperator interface for the system may be of several types, including aground control station (GCS) 19 having graphical and numerical displays21, keyboards 23, mouse 25 or similar input device, and audio/videocomponents, as shown in FIG. 3. Another example of the interface is aflight control box (FCB) 27, as shown in FIG. 4, having a set ofjoysticks 29 or similar tactile input devices and graphical displays 31.Aircraft 11 may be operated by one or more operators, with each operatorusing one of the operator interface devices. To illustrate the operationof the system of the invention, the system is described herein ascomprising GCS 19 and FCB 27 for controlling aircraft 11.

The basic mode of the system allows both the operators of GCS 19 and FCB27 to command the velocity of aircraft 11 relative to ship 13. Either ofthe operators can command the relative velocity from hover to themaximum airplane value, and GCS 19 can switch control back and forthfrom GCS 19 to FCB 27 as desired.

The major components of the system are shown in FIG. 5. Componentscarried on aircraft 11 are denoted by bracket 33, and components carriedon ship, or reference vehicle, 13 are denoted by bracket 35.

On aircraft 11, a Global Positioning System (GPS) receiver module 37receives transmitted signals 39, 41 from orbiting GPS satellites,allowing GPS module 37 to determine the position of aircraft 11 inrelation to the earth. Also, inertial movement sensors 43, which may beaccelerometers, measure the movement of aircraft 11 in three orthogonalaxes, and a data receiver 45 receives data transmitted to aircraft 11from components 35 on ship 13 and from GCS 19 and/or FCB 27.

On ship 13, a GPS receiver module 47 also receives GPS satellite signals(not shown) and determines the position of ship 13 relative to theearth, and inertial movement sensors 49 measure the movement of ship 13.These data sources are combined to generate position and velocity datafor ship 13, and the data is then sent in a transmission signal 51 todata receiver 45 of aircraft 11 using transmitter 53.

While not required to be located on the reference vehicle, GCS 19 andFCB 27 are typically located on ship 13. GCS 19 and/or FCB 27 send adata transmission 55 to aircraft 11 for providing flight-controlcommands to aircraft 11. As discussed below, transmission 55communicates the selected position and/or velocity of aircraft relativeto ship 13 that the operator desires for aircraft 11 to attain andmaintain until a new command is given. In some embodiments,transmissions 51 and 55 may be sent using the same transmitter, forexample, transmitter 53. In addition, in those embodiments in whichaircraft 11 is a manned aircraft, the pilot may transmit or otherwiseinput this transmitted data.

Data receiver 45 of aircraft 11 receives transmissions 51 and 55, andthe transmitted data is routed to a digital control system 57 carried onaircraft 11. Additionally, the sensed data from GPS module 37 andsensors 43 are routed to control system 57, and control system 57calculates the position and velocity of aircraft 11 in relation to theearth, as well as the position and velocity of aircraft 11 relative tothe reference vehicle, which is ship 13. This calculated relativeposition and relative velocity is compared with the selected positionand/or selected velocity communicated in transmission 55, and an amountof error is determined. Control system 57 then commands variousflight-control devices on aircraft 11, such as throttle 59 and rudder61, to maneuver aircraft so as to minimize, and preferably eliminate,the error between the calculated and selected values. Other flightcontrol devices commanded by control system 57 may include, as shown,ailerons 63, flaps 65, engine nacelles 67, or other flight controldevices 69, including cyclic controls for rotors and blade angleactuators for propellers.

A key advantage of the present invention is that aircraft 11 iscontrolled relative to the reference vehicle and can be commanded tomove in the direction that the controls of GCS 19 or FCB 27 are moved.The response is independent of the azimuth orientation of aircraft 11.For example, if the operator wants the aircraft to move in the +Xdirection relative to the reference vehicle, then he will enter thedesired system mode and move the X controller, such as one of joysticks29 on FCB 27 (FIG. 4) or a graphical icon on a display of GCS 19 (FIG.3), in the +X direction, and the commanded variable (position orvelocity) relative to ship 13 will be changed in the X direction. Thisalso applies to Y and Z directions.

FIGS. 6 and 7 illustrate two coordinate systems that can be used whencontrolling aircraft 11. FIG. 6 shows a polar-coordinate, plan-viewgraphical display 71 that may be used by GCS 19 to send relativevelocity commands to aircraft 11. Display 71 includes a referencevehicle icon 73, which represents ship 13, in the center of concentriccircles 74. The heading of ship 13 relative to due north is indicated bythe rotation of icon 73 in relation to a 360-degree compass 75 depictedon concentric circles 74. A Cartesian coordinate system relative to ship13 is depicted as axes 77 and 79, wherein axis 77 is aligned with thecurrent heading of ship 13 and icon 73, and axis 79 is perpendicular toaxis 77. A line 81 points to the actual current location of aircraft 11relative to ship 13. As shown in the example of FIG. 6, line 81indicates that aircraft 11 is actually located a distance behind andslightly to the right of ship 13.

A vector 83 indicates the aircraft velocity (both magnitude anddirection) relative to the velocity of ship 13. A small circle 85indicates the desired terminus of the velocity commanded by GCS 19.Circle 85 will be centered at the outer end of vector 83 when the actualvelocity of aircraft 11 relative to ship 13 is equal to the desiredvelocity of aircraft 11 relative to ship 13. Concentric circles 74 ofdisplay 71 indicate selected values of the magnitude of relativevelocity. This magnitude increases as the velocity vector extendsfarther from the center of display 71. Because display 71 represents apolar-coordinate command system, the magnitude of the relative velocitywill not be negative. This configuration allows the heading of ship 13,the commanded relative velocity of aircraft 11, and the actual relativevelocity of aircraft 11 to be quickly and easily ascertained by simplyviewing display 71. Should a GCS operator want to change the velocity ofaircraft 11 relative to ship 13, he simply clicks on circle 85 and dragscircle 85 to the location on display 71 that represents the new relativevelocity. This commanded, or selected, relative velocity is thentransmitted to aircraft 11, which is commanded by control system 57(FIG. 5) to make the necessary flight control adjustments to attain andmaintain the commanded relative velocity. By commanding aircraft 11 toattain a relative velocity of zero, aircraft 11 will hold its positionrelative to ship 13.

It should be appreciated that the system for manipulating icons ondisplay 71 may include semi-automated actions, or shortcuts, that areprogrammed into the system. For example, the system may have a shortcutthat allows the operator to command aircraft 11 to have zero relativevelocity by right-clicking with a mouse or other input device atselected locations within display 71.

The advantages provided by command display 71 when controlling therelative velocity of aircraft 11 are that the operator can command therelative velocity vector with one simple action, and he can also see thevelocity of aircraft 11 relative to this velocity command. With onesmall display, the operator can have situational awareness and commandcontrol, plus observe all of the following information: (1) the shipheading direction relative to the compass; (2) the direction of theaircraft position relative to the ship; (3) the direction of theaircraft velocity relative to the ship; (4) the magnitude of theaircraft velocity relative to the ship; (5) the magnitude of thecommanded velocity relative to the ship; and (6) the direction of thecommanded velocity relative to the ship.

Though described above as used for controlling velocity,polar-coordinate display 71 may alternatively be configured to allowpositioning of aircraft 11 relative to ship 13, though this ispreferably used only when aircraft 11 is located far from ship 13.During such use, an icon (not shown) representing the position ofaircraft 11 can be dragged to the desired location on display 71relative to ship 13, and aircraft 11 may have a zero relative velocity,i.e., station-keeping, or a selected relative velocity to resume fromthe commanded position. When used for position commands, concentriccircles 74 on display 71 act as range, or radius, indicators. Shown inFIG. 6 is a triangular icon 87 that indicates a preprogrammed stationpoint that is set up to be relative to ship 13, shown here as being adistance directly behind ship 13.

A Cartesian-coordinate, plan-view display 89 on GCS 19 is shown in FIG.7. The Cartesian coordinates are preferably used only when aircraft 11is near to ship 13. An icon 91 represents aircraft 11 on approach to arepresentation of TDP 93 on deck 95 of ship 13. The coordinates are inthe X, Y system, with a range guide 97 indicating distance from TDP 93.Display 89 may be configured to allow the operator of GCS 19 tomanipulate icon 91 for controlling the movement of aircraft 11 bydragging icon 91 relative to ship 13, as represented by deck 95.Alternatively, display 89 may be configured as an information-onlydisplay, which does not allow direct control of aircraft 11 bymanipulating icon 91.

The operator of FCB 27 can also command aircraft 11 in either the polaror Cartesian coordinates after control has been transferred from GCS 19to the FCB 27. When control is switched to the FCB, the joysticks 29will be in the centered position, which will command the relativevelocity to remain at its present value. This means that aircraft 11will continue with the same velocity relative to ship 13, and in thesame direction until the FCB operator commands a relative velocitychange. The FCB operator can command an increase or decrease in velocityby moving a longitudinal joystick forward or rearward, respectively, andthe velocity command will change proportional to stick displacement.When in polar mode, the direction of the velocity can be changed bymoving a lateral joystick on FCB 27, such that left and right lateralstick motion will command the velocity vector to rotate in thecounterclockwise and clockwise directions, respectively, at a rateproportional to stick displacement.

The operator of FCB 27 also has the capability to fly the aircraft bycommanding velocity in the ship coordinate system, which is an X, Ysystem. This mode is required for manually positioning the aircraft overthe deck, or TDP, of the moving ship, or performing manual landings. Theforward and rearward movement of the longitudinal joystick will commandvelocity in the X direction (fore and aft on the ship deck), and theright or left movement of the lateral joystick will command a velocityin the Y direction (port and starboard on the ship deck). The forwardmotion on the controller will preferably command a velocity toward therear of the deck, and a right motion will preferably command a velocitytoward the port side of the deck. When the joysticks are centered,aircraft 11 will be commanded to hold its present position relative tothe TDP. These conventions were chosen because the operator of FCB 27will be facing toward the rear of the deck as aircraft 11 approaches,and this convention will move aircraft 11 the same direction as thestick motions. Velocities are commanded in the X, Y coordinate systeminstead of in the aircraft axes in order to make the commandsindependent of the heading of aircraft 11.

One application that is particularly well suited for the control systemof the invention is maneuvering an aircraft into an acquisition windowfor another control system. For example, the aircraft may be maneuveredinto a window for acquisition by an auto-recovery or landing system.

FIG. 8 is a flowchart illustrating the method of relative-velocitycontrol of the system of the invention. The method begins with step 99,in which the sensor system carried on an aircraft determines theposition and velocity of the aircraft relative to the earth. In step101, the aircraft receives a data transmission communicating theposition and velocity of a reference vehicle, which is used in step 103with the sensed data from step 99 to calculate the velocity and/orposition of the aircraft relative to the reference vehicle.Flight-control devices are commanded in step 105 so as to fly theaircraft to a desired relative velocity and/or position. An optionalstep 107 is also shown in which transmitted data communicating thedesired relative velocity and/or position is received by the aircraft.

An additional advantage of the control system of the invention is thatit allows for control of aircraft 11 using various autonomous andsemi-autonomous modes, including:

1. Auto-recovery: In this mode, the operator maneuvers aircraft 11 intoan acquisition window, then commands the auto-recovery system to landaircraft 11 on the TDP. An X,Y,Z coordinate system is defined with thepositive X axis out the stern of the ship, with the option of rotationto a specified approach angle. Y is positive out the starboard side, andZ is positive in the up direction. Once acquired, the sensors on ship 13track aircraft 11, and three-dimensional position data are sent to GCS19, which in turn transmits these positions to aircraft 11.

2. Auto-approach: The approach phase commands the aircraft to follow apreset approach profile from its present location to a point over theTDP. The approach profile specifies a velocity in the X direction and Zposition (height) as functions of distance from the TDP. The approachprofile requires the aircraft Y position to go to zero and hold at zerothroughout the approach, meaning aircraft 11 is aligned with the desiredapproach angle to ship 13. When the aircraft has arrived near the TDP, aposition-hold function will be engaged to hold aircraft 11 in a hoverover the TDP.

3. Deck Following: After the position hold is engaged, aircraft 11 canbe commanded to start following the deck surge heave and sway motions,keeping aircraft 11 in a selected position relative to the TDP.

4. Descend to the Deck: Descend to the deck is the final phase ofauto-recovery, in which aircraft 11 is commanded to descend at aspecified rate relative to the TDP.

5. Waveoff/Abort: If the operator of the GCS 19 or FCB 27 chooses,aircraft 11 can be commanded to waveoff, and it will execute apredetermined maneuver to move away from ship 13. Aircraft 11 moves inthe positive X direction (to the rear of ship 13) and enters a gentlevertical climb for a predetermined period of time after which therelative velocity vector is commanded to zero and the aircraft altitudeis held at its then present value.

An abort is automatically entered if failure management logic of thecontrol system determines that the auto-recovery cannot be completed.The reasons for abort may include excessive position or velocity errors,failures or loss of parts of the control system, and loss of datauplink. The control of aircraft 11 during an abort is preferably thesame as for a waveoff, the only difference being that an abort isinitiated automatically and a waveoff is initiated by the GCS or FCBoperator.

6. Fly-To-Station: The Fly-to-Station mode allows the GCS operator tospecify a point at a distance and direction from ship 13 to whichaircraft 11 will fly automatically. Aircraft 11 accelerates to aprescheduled velocity profile, flies to the designated location,decelerates and stops at that location. It then holds relative positionthere until commanded to do otherwise. This mode is a convenient way ofcommanding the aircraft to fly to the acquisition window, from which theaircraft is acquired, and the auto-recovery is initiated. This type ofmode may also be used automatically to send aircraft 11 to apredetermined location and fight path if data communication is lost.

The present invention provides significant advantages over the priorart, including: (1) the autonomous control of aircraft that commands theaircraft to attain and maintain the selected position and/or velocity ofthe aircraft relative to the reference vehicle by comparing values fromonboard sensors with data transmitted to the aircraft indicating thevelocity and position of the reference vehicle; (2) the easy control ofaircraft relative to a moving vehicle without the operator having toconsider the position or velocity of the aircraft in relation to theearth; (3) the control of the velocity of the aircraft relative to thereference vehicle by manipulating a representation of the terminus ofthe relative velocity vector on a graphical display to a desired angleand magnitude relative to the velocity of the reference vehicle; (4) thecontrol of the position and/or velocity of the aircraft relative to thereference vehicle by manipulating tactile input devices, such asjoysticks.

While this invention has been described with reference to illustrativeembodiments, this description is not intended to be construed in alimiting sense. Various modifications and combinations of theillustrative embodiments, as well as other embodiments of the invention,will be apparent to persons skilled in the art upon reference to thedescription.

1. A system for controlling flight of an aircraft comprising: a sensorsystem disposed on the aircraft for sensing a position of the aircraftand an inertial movement of the aircraft, the sensor system beingadapted to communicate sensed data representing the position and theinertial movement of the aircraft; a receiver disposed on the aircraftand adapted to receive transmitted reference data communicating aposition and movement of a reference vehicle; commanded datarepresenting a selected velocity of the aircraft relative to thereference vehicle; and a control system disposed on the aircraft forcalculating a calculated velocity of the aircraft relative to thereference vehicle using the sensed data and the reference data and forcontrolling flight-control devices on the aircraft, such that theaircraft attains and maintains a selected velocity relative to thereference vehicle corresponding to the commanded data; wherein thecommanded data is inputted prior to flight of the aircraft, into thecontrol system communicating a selected position and velocity of theaircraft relative to the reference vehicle.
 2. The system according toclaim 1, wherein the receiver is further adapted to receive atransmission communicating the commanded data.
 3. The system accordingto claim 2, wherein the commanded data is transmitted from the referencevehicle.
 4. The system according to claim 1, wherein the transmitteddata communicating the position and movement of the reference vehicleare transmitted from the reference vehicle.
 5. The system according toclaim 1, wherein the sensor system determines the position of theaircraft using a Global Positioning System receiver module.
 6. A systemfor controlling the flight of an aircraft comprising: sensors carried onthe aircraft, the sensors being adapted to determine the position of theaircraft relative to the earth and the inertial movement of theaircraft, the sensors also being adapted to output data communicatingthe position and movement of the aircraft; a receiver carried on theaircraft and adapted to receive transmitted data communicating theposition of a reference vehicle relative to the earth and movement ofthe reference vehicle relative to the earth; and a control systemcarried on the aircraft and connected to the sensors and the receiver,the control system calculating the position of the aircraft relative tothe reference vehicle and movement of the aircraft relative to thereference vehicle using the data from the sensors, commanded datainputted into the control system prior to flight, and the data receivedby the receiver, the control system being adapted to commandflight-control devices on the aircraft for causing the aircraft tomaneuver in a manner that attains and maintains a selected positionrelative to the reference vehicle or a selected velocity relative to thereference vehicle.
 7. The system according to claim 6, wherein thereceiver is adapted to receive data communicating the selected positionand velocity of the aircraft relative to the reference vehicle.
 8. Thesystem according to claim 7, wherein the data communicating the selectedposition and velocity of the aircraft relative to the reference vehicleis transmitted from the reference vehicle.
 9. The system according toclaim 6, wherein the data communicating the position and movement of thereference vehicle is transmitted from the reference vehicle.
 10. Thesystem according to claim 6, wherein the sensors determine the positionof the aircraft using a Global Positioning System receiver module.
 11. Amethod of controlling the flight of an aircraft, the method comprisingthe steps of: (a) prior to flight of the aircraft, inputting into acontrol system data communicating a selected position and velocity ofthe aircraft relative to a reference vehicle; (b) determining a positionof the aircraft relative to the earth and an inertial movement of theaircraft using sensors carried on the aircraft; (c) receivingtransmitted data communicating a position of the reference vehiclerelative to the earth and a movement of the reference vehicle relativeto the earth using a receiver carried on the aircraft; (d) using acontrol system carried on the aircraft to calculate a velocity of theaircraft relative to the reference vehicle by comparing data from thesensors and the transmitted data; and (e) commanding flight-controldevices on the aircraft with the control system, thereby causing theaircraft to attain and maintain the selected velocity relative to thereference vehicle.
 12. The method according to claim 11, furthercomprising the step of: prior to step (e), receiving with the receiver atransmission containing data communicating the selected position andvelocity of the aircraft relative to the reference vehicle.
 13. Themethod according to claim 12, further comprising the step of:transmitting from the reference vehicle the transmission communicatingthe selected position and velocity of the aircraft relative to thereference vehicle.
 14. The method according to claim 11, furthercomprising the step of: prior to step (c), transmitting the datacommunicating the position and movement of the reference vehicle fromthe reference vehicle.
 15. A multi-vehicle system comprising: areference vehicle; at least one aircraft; a reference sensor systemcarried on the reference vehicle and adapted to determine the positionrelative to the earth and the movement relative to the earth of thereference vehicle; an aircraft sensor system carried on each aircraftand adapted to determine the position relative to the earth and theinertial movement of each corresponding aircraft; a receiver carried oneach aircraft for receiving transmitted data communicating the positionand movement of the reference vehicle; a control system carried on eachaircraft adapted to calculate the velocity of each correspondingaircraft relative to the reference vehicle and adapted to commandflight-control devices for causing each corresponding aircraft to fly ata selected velocity relative to the reference vehicle; and commandeddata inputted prior to flight of the aircraft into the control systemcommunicating a selected position and velocity of the aircraft relativeto the reference vehicle.
 16. The multi-vehicle system according toclaim 15 wherein the reference vehicle is a second aircraft.